Wearable-device-measured physical activity and future health risk

Abstract

Use of wearable devices that monitor physical activity is projected to increase more than fivefold per half-decade¹. We investigated how device-based physical activity energy expenditure (PAEE) and different intensity profiles were associated with all-cause mortality. We used a network harmonization approach to map dominant-wrist acceleration to PAEE in 96,476 UK Biobank participants (mean age 62 years, 56% female). We also calculated the fraction of PAEE accumulated from moderate-to-vigorous-intensity physical activity (MVPA). Over the median 3.1-year follow-up period (302,526 person-years), 732 deaths were recorded. Higher PAEE was associated with a lower hazard of all-cause mortality for a constant fraction of MVPA (for example, 21% (95% confidence interval 4-35%) lower hazard for 20 versus 15 kJ kg^-1 d^-1 PAEE with 10% from MVPA). Similarly, a higher MVPA fraction was associated with a lower hazard when PAEE remained constant (for example, 30% (8-47%) lower hazard when 20% versus 10% of a fixed 15 kJ kg^-1 d^-1 PAEE volume was from MVPA). Our results show that higher volumes of PAEE are associated with reduced mortality rates, and achieving the same volume through higher-intensity activity is associated with greater reductions than through lower-intensity activity. The linkage of device-measured activity to energy expenditure creates a framework for using wearables for personalized prevention.

Figure 1

Overview of methods with selected descriptive statistics. MVPA: moderate-to-vigorous physical activity.

Figure 2

Adjusted hazard ratios of all-cause mortality comparing (a) different volumes of physical activity energy expenditure and (b) different fractions of physical activity energy expenditure from moderate-to-vigorous physical activity, adjusted for physical activity energy expenditure. Adjusted hazard ratios and histogram data shown for values inside the 1^st or 99^th percentiles of the physical activity energy expenditure distribution amongst those who died.

Figure 3

Hazard ratios of all-cause mortality according to the joint distribution of physical activity energy expenditure and the fraction from moderate-to-vigorous physical activity, relative to a physical activity energy expenditure of 15kJ/kg/day and 10% fraction of moderate-to-vigorous physical activity. MVPA: moderate-to-vigorous physical activity. (n=96,476).

Figure 4

The relative risk of mortality for combinations of physical activity energy expenditure and the fraction that came from moderate-to-vigorous physical activity. MVPA: Moderate-to-vigorous physical activity. Adjusted hazard ratio for mortality represented by the colour gradient with 15 kJ/kg/day and 10% as reference values. Size of the points represents sample size and segments indicate the average minutes of unbouted MVPA for each combination. Lines divide groups of similar observed median values of MVPA time, as indicated by the text. Each data point represents categories of dimensions 2.5 kJ/kg/day * 2.5%. Data points are placed at the midpoint of these categories. Points are not shown if there were no deaths for that combination. (n=96,476).